Migrations are not auto-applied on startup (Program.cs:856 is commented),
so dev/prod DBs need this applied manually. Idempotent (guarded by
__EFMigrationsHistory checks) — safe to run regardless of current state.
Adds CompanyPreferences.Default{Revenue,Cogs,Inventory}AccountId + indexes + FKs.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
